Question

The meaning life expectancy of a light bulb is 895 hours with a standard deviation of 18 hours. What is the approximate standard deviation of the mean for all samples with n = 40?
A 0.60 h
B 2.22 h
C 2.85 h
D 0.45 h

Answer 1

@kropot72

Answer 2

The sample size is greater than 30. Therefore we can make use of the Central Limit Theorem and regard the distribution of the sample means as Normal.The standard deviation of the sample mean X-bar is found from:
\[\large \bar{X}=\frac{\sigma}{\sqrt{n}}\]
where sigma is the population standard deviation.

Answer 3

@NightMath Can you do the calculation now?